The water pollution problem in the food-processing industry (including particularly meat-packing houses, slaughtering houses, meat canning, and the like meat processing operations) is becoming more and more serious as new regulations are being imposed and existing regulations strictly enforced. Present regulations impose a "surcharge" on BOD and suspended solids and limit oils and grease to 100 ppm. Proposed regulations under the federal NPDES (National Pollutant Discharge Elimination System) program will put limits on BOD, suspended solids, and oils and grease which are substantially lower than present standards. The cleanup of equipment used in this industry generates waste waters which characteristically contain significant amounts of fats and greases (mainly, mixed triglycerides) of animal or plant origin, sometimes termed hexane solubles, as well as miscellaneous contaminants, such as cleaning agents, surfactants, alkalies, acidic materials, and the like. Such waste waters contain both suspended and dissolved solids and tend to be quite stable, and such waters characteristically contain levels and impurities far above those permitted under present federal and state pollution standards. Thus, such waste waters must be treated to clean them up sufficiently for discharge into sewers of conventional sanitation systems.
The task of clarifying and purifying such waste waters, at least to an extent sufficient to produce a product water which meets the minimum standards for sewering, constitutes a major problem particularly when such task is to be accomplished in an economical practical and reliable manner. Heretofore, the art has commonly attempted to effectuate a separation of water from animal derived fatty materials using gravity separation devices which are dependent upon differences in the specific gravity of water relative to animal fats and greases in admixture therewith. Thus, it is contemporarily common to find in conjunction with food-processing operation, a so-called grease pit into which waste waters from such operation are discharged. Such a grease pit as often as once a day may be cleaned manually by skimming to remove floating solids. Waters passing through the grease pit are simply routinely sewered. Available evidence indicates, however, that during cleanup periods such a grease pit cleanup water can commonly contain more materials (usually in an emulsified form) than was present in the initial input waste water, and such emulsified materials may be more stable than the initial fatty waste water. Simple gravity separation is inadequate to meet conventional effluent requirements.
Perhaps the most prevalent system currently on the market is Dissolved Air Flotation. This system can meet the effluent quality requirements, however large qualities of sludge are produced which need additional treatment to avoid exorbitant waste disposal costs. These systems also require chemical pretreatment, surge tanks, pumps, controls, and large amounts of space which result in an expensive and complicated operation.
A pollution control system designed for this industry must consider all of the following factors:
1. The waste stream from the plant will vary in flow rates, temperature, pH and composition.
2. The effluent from the treatment system should meet the present MSD criteria and the proposed 1977 Federal guidelines.
3. The sludge from the system should be relatively dry and free of excess water to reduce operating costs, eliminate additional treatment, and facilitate handling.
4. The unit should be fully automatic to reduce labor and minimize operational errors.
5. The unit should be compact and suitable for outdoor installation as space is at a premium.
6. The initial cost, installation cost and operating costs must be reasonable.
Prior to the present invention, no single prior art unit or system could meet all of the above considerations.
While various systems for animal fat and grease removal from water have been postulated, such systems typically suffer from a number of disadvantages, such as high initial cost and operational costs, complicated equipment and process sequences, excessive sensitivity to variations in composition of starting waste water, excessive space requirements, and the like. There is a great need in the art for a compact, reliable, relatively simple, relatively low cost system suitable for handling treatments of waste waters from food-processing operations.